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.