scsi: megaraid_sas: Fix for a potential deadlock

In the Linux kernel, the following vulnerability has been resolved:

scsi: megaraid_sas: Fix for a potential deadlock

This fixes a 'possible circular locking dependency detected' warning

CPU0 CPU1

---- ----

lock(&instance->reset_mutex);

lock(&shost->scan_mutex);

lock(&instance->reset_mutex);

lock(&shost->scan_mutex);

Fix this by temporarily releasing the reset_mutex.