selftests/mm: use long for dwRegionSize

selftests/mm: use long for dwRegionSize

Change the type of 'dwRegionSize' in wp_init() and wp_free() from int to
long to match callers that pass long or unsigned long long values.

wp_addr_range function is left unchanged because it passes 'dwRegionSize'
parameter directly to pagemap_ioctl, which expects an int.

This patch does not fix any actual known issues.  It aligns parameter
types with their actual usage and avoids any potential future issues.

Link: https://lkml.kernel.org/r/20250427102639.39978-1-siddarthsgml@gmail.com
Signed-off-by: Siddarth G <siddarthsgml@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>