scsi: lpfc: Prevent lpfc_debugfs_lockstat_write() buffer overflow

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

scsi: lpfc: Prevent lpfc_debugfs_lockstat_write() buffer overflow

A static code analysis tool flagged the possibility of buffer overflow when

using copy_from_user() for a debugfs entry.

Currently, it is possible that copy_from_user() copies more bytes than what

would fit in the mybuf char array. Add a min() restriction check between

sizeof(mybuf) - 1 and nbytes passed from the userspace buffer to protect

against buffer overflow.