Kdbg search resource leak fixes

Coverity ID 1237209: Unsigned compared against 0 (NO_EFFECT)unsigned_compare: This greater-than-or-equal-to-zero comparison of an unsigned value is always true. page_paddr + step >= 0UL
Coverity ID 1237202: Unchecked return value (CHECKED_RETURN)7. check_return: Calling driver_get_vcpureg without checking return value (as is done elsewhere 13 out of 16 times).
Coverity ID 1237215: Resource leak (RESOURCE_LEAK)10. leaked_storage: Variable bm64 going out of scope leaks the storage it points to.
Coverity ID 1237216: Resource leak (RESOURCE_LEAK)16. leaked_storage: Variable bm32 going out of scope leaks the storage it points to.
Coverity ID 1237218: Resource leak (RESOURCE_LEAK)8. leaked_storage: Variable bm going out of scope leaks the storage it points to.