Fix serail stall when too-fast baud rates attempted

teensy3/serial1.c

 		#endif
 	}
 #if defined(HAS_KINETISK_UART0)
+	if (divisor < 32) divisor = 32;
 	UART0_BDH = (divisor >> 13) & 0x1F;
 	UART0_BDL = (divisor >> 5) & 0xFF;
 	UART0_C4 = divisor & 0x1F;
 	UART0_PFIFO = 0;
 #endif
 #elif defined(HAS_KINETISL_UART0)
+	if (divisor < 1) divisor = 1;
 	UART0_BDH = (divisor >> 8) & 0x1F;
 	UART0_BDL = divisor & 0xFF;
 	UART0_C1 = 0;

teensy3/serial2.c

 	CORE_PIN10_CONFIG = PORT_PCR_DSE | PORT_PCR_SRE | PORT_PCR_MUX(3);
 #endif
 #if defined(HAS_KINETISK_UART1)
+	if (divisor < 32) divisor = 32;
 	UART1_BDH = (divisor >> 13) & 0x1F;
 	UART1_BDL = (divisor >> 5) & 0xFF;
 	UART1_C4 = divisor & 0x1F;
 	UART1_PFIFO = 0;
 #endif
 #elif defined(HAS_KINETISL_UART1)
+	if (divisor < 1) divisor = 1;
 	UART1_BDH = (divisor >> 8) & 0x1F;
 	UART1_BDL = divisor & 0xFF;
 	UART1_C1 = 0;

teensy3/serial3.c

 	}
 #endif
 #if defined(HAS_KINETISK_UART2)
+	if (divisor < 32) divisor = 32;
 	UART2_BDH = (divisor >> 13) & 0x1F;
 	UART2_BDL = (divisor >> 5) & 0xFF;
 	UART2_C4 = divisor & 0x1F;
 	UART2_C1 = 0;
 	UART2_PFIFO = 0;
 #elif defined(HAS_KINETISL_UART2)
+	if (divisor < 1) divisor = 1;
 	UART2_BDH = (divisor >> 8) & 0x1F;
 	UART2_BDL = divisor & 0xFF;
 	UART2_C1 = 0;

teensy3/serial4.c

 		case 32: CORE_PIN32_CONFIG = PORT_PCR_DSE | PORT_PCR_SRE | PORT_PCR_MUX(3); break;
 		case 62: CORE_PIN62_CONFIG = PORT_PCR_DSE | PORT_PCR_SRE | PORT_PCR_MUX(3); break;
 	}
+	if (divisor < 32) divisor = 32;
 	UART3_BDH = (divisor >> 13) & 0x1F;
 	UART3_BDL = (divisor >> 5) & 0xFF;
 	UART3_C4 = divisor & 0x1F;

teensy3/serial5.c

 	transmitting = 0;
 	CORE_PIN34_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_PFE | PORT_PCR_MUX(3);
 	CORE_PIN33_CONFIG = PORT_PCR_DSE | PORT_PCR_SRE | PORT_PCR_MUX(3);
+	if (divisor < 32) divisor = 32;
 	UART4_BDH = (divisor >> 13) & 0x1F;
 	UART4_BDL = (divisor >> 5) & 0xFF;
 	UART4_C4 = divisor & 0x1F;

teensy3/serial6.c

 	transmitting = 0;
 	CORE_PIN47_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_PFE | PORT_PCR_MUX(3);
 	CORE_PIN48_CONFIG = PORT_PCR_DSE | PORT_PCR_SRE | PORT_PCR_MUX(3);
+	if (divisor < 32) divisor = 32;
 	UART5_BDH = (divisor >> 13) & 0x1F;
 	UART5_BDL = (divisor >> 5) & 0xFF;
 	UART5_C4 = divisor & 0x1F;