scsi: smartpqi: Replace kmalloc() + copy_from_user() with memdup_user()

Replace kmalloc() followed by copy_from_user() with memdup_user() to
simplify and improve pqi_passthru_ioctl().

Since memdup_user() already allocates memory, use kzalloc() in the else
branch instead of manually zeroing 'kernel_buffer' using memset(0).

Return early if an error occurs.  No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Acked-by: Don Brace <don.brace@microchip.com>
Message-Id: <20250922201832.1697874-2-thorsten.blum@linux.dev>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>