mm: vrealloc: fix missing nommu implementation

mm: vrealloc: fix missing nommu implementation

Commit 5ec6d992f460 ("mm: vmalloc: implement vrealloc()") introduces
vrealloc(), but lacks the implementation of the nommu version of this
function.

Note that currently nommu isn't actually broken without this.  The only
user, kvrealloc(), never actually calls into vrealloc() with nommu, since
it's guarded by is_vmalloc_addr(), which for nommu always returns false.

However, since this becomes a real issue once vrealloc() is used by other
code, fix this.

Link: https://lkml.kernel.org/r/20240725141227.13954-1-dakr@kernel.org
Fixes: 5ec6d992f460 ("mm: vmalloc: implement vrealloc()")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>