initramfs: avoid static buffer for error message

initramfs: avoid static buffer for error message

The dynamic error message printed if CONFIG_RD_$ALG compression support
is missing needn't be propagated up to the caller via a static buffer.
Print it immediately via pr_err() and set @message to a const string to
flag error.

Before:
   text    data     bss     dec     hex filename
   8006    1118       8    9132    23ac init/initramfs.o

After:
   text    data     bss     dec     hex filename
   7938    1022       8    8968    2308 init/initramfs.o

Signed-off-by: David Disseldorp <ddiss@suse.de>
Link: https://lore.kernel.org/r/20250304061020.9815-9-ddiss@suse.de
Signed-off-by: Christian Brauner <brauner@kernel.org>