bpf: Fix BPF_INTERNAL namespace import

The commit cdd30eb ("module: Convert symbol namespace to string
literal") makes the grammar of MODULE_IMPORT_NS and EXPORT_SYMBOL_NS
different between the stable branches and the mainline.  But when
the commit 955f9ed ("bpf: Add namespace to BPF internal symbols")
was backported from mainline, only EXPORT_SYMBOL_NS instances are
adapted, leaving the MODULE_IMPORT_NS instance with the "new" grammar
and causing the module fails to build:

    ERROR: modpost: module bpf_preload uses symbol bpf_link_get_from_fd from namespace BPF_INTERNAL, but does not import it.
    ERROR: modpost: module bpf_preload uses symbol kern_sys_bpf from namespace BPF_INTERNAL, but does not import it.

Reported-by: Mingcong Bai <jeffbai@aosc.io>
Reported-by: Alex Davis <alex47794@gmail.com>
Closes: https://lore.kernel.org/all/CADiockBKBQTVqjA5G+RJ9LBwnEnZ8o0odYnL=LBZ_7QN=_SZ7A@mail.gmail.com/
Fixes: 955f9ed ("bpf: Add namespace to BPF internal symbols")
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: xry111

kernel/bpf/preload/bpf_preload_kern.c

@@ -89,5 +89,5 @@ static void __exit fini(void)
 }
 late_initcall(load);
 module_exit(fini);
-MODULE_IMPORT_NS("BPF_INTERNAL");
+MODULE_IMPORT_NS(BPF_INTERNAL);
 MODULE_LICENSE("GPL");