pci(4): don't perform maximum register number check

Different sub-kinds of PCI buses may have different rules and
thus it is up for the bus backends to do proper input checks.
For example, PCIe allows configuration register numbers < 0x1000,
while for PCI proper the limit is 0x100.
And, in fact, the buses already do the checks.

Reviewed by:	jhb
MFC after:	1 week
X-ToDo:		add check for negative value to bus backends
X-ToDo:		use named constant for maximum PCIe register

sys/dev/pci/pci_user.c

@@ -605,9 +605,8 @@ getconfexit:
 		case 4:
 		case 2:
 		case 1:
-			/* Make sure register is in bounds and aligned. */
+			/* Make sure register is not negative and aligned. */
 			if (io->pi_reg < 0 ||
-			    io->pi_reg + io->pi_width > PCI_REGMAX + 1 ||
 			    io->pi_reg & (io->pi_width - 1)) {
 				error = EINVAL;
 				break;