LU-18876 misc: make dbgcksum_file_name static

LU-18876 misc: make dbgcksum_file_name static

The global variable dbgcksum_file_name is defined
twice: once in OSC and another time in target. This
causes a linker error when the Lustre modules are
compiled into the static kernel image.

Resolve this by making both instances local to
the functions that require them using
OBD_ALLOC()/FREE().

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I37ac4c60754082561a65e61ab2d956d68555394f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58629
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>