x86/boot: fix early error output

x86/boot: fix early error output

In 9180f5365524 a change was made to the send_chr function to take in
C-strings and output a character at a time until a NULL was encountered.
However, when there is no VGA there is no code to increment the current
character position resulting in an endless loop of the first character.
This moves the (implicit) increment such that it occurs in all cases.

Signed-off-by: David Esler <drumandstrum@gmail.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>
[jb: correct title and description]
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>