scsi: qla2xxx: Avoid triggering undefined behavior in qla2x00_mbx_completion()

A left shift must shift less than the bit width of the left argument.
Avoid triggering undefined behavior if ha->mbx_count == 32.

This patch avoids that UBSAN reports the following complaint:

UBSAN: Undefined behaviour in drivers/scsi/qla2xxx/qla_isr.c:275:14
shift exponent 32 is too large for 32-bit type 'int'
Call Trace:
 dump_stack+0x4e/0x6c
 ubsan_epilogue+0xd/0x3b
 __ubsan_handle_shift_out_of_bounds+0x112/0x14c
 qla2x00_mbx_completion+0x1c5/0x25d [qla2xxx]
 qla2300_intr_handler+0x1ea/0x3bb [qla2xxx]
 qla2x00_mailbox_command+0x77b/0x139a [qla2xxx]
 qla2x00_mbx_reg_test+0x83/0x114 [qla2xxx]
 qla2x00_chip_diag+0x354/0x45f [qla2xxx]
 qla2x00_initialize_adapter+0x2c2/0xa4e [qla2xxx]
 qla2x00_probe_one+0x1681/0x392e [qla2xxx]
 pci_device_probe+0x10b/0x1f1
 driver_probe_device+0x21f/0x3a4
 __driver_attach+0xa9/0xe1
 bus_for_each_dev+0x6e/0xb5
 driver_attach+0x22/0x3c
 bus_add_driver+0x1d1/0x2ae
 driver_register+0x78/0x130
 __pci_register_driver+0x75/0xa8
 qla2x00_module_init+0x21b/0x267 [qla2xxx]
 do_one_initcall+0x5a/0x1e2
 do_init_module+0x9d/0x285
 load_module+0x20db/0x38e3
 SYSC_finit_module+0xa8/0xbc
 SyS_finit_module+0x9/0xb
 do_syscall_64+0x77/0x271
 entry_SYSCALL64_slow_path+0x25/0x25

Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Himanshu Madhani <himanshu.madhani@cavium.com>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Acked-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>