boot/shim: fix build issue due to gnu-efi

boot/shim: fix build issue due to gnu-efi

shim fails to build with:

console.c:448:5: error: ‘EFI_WARN_UNKOWN_GLYPH’ undeclared here (not in a function); did you mean ‘EFI_WARN_UNKNOWN_GLYPH’?
  448 |  {  EFI_WARN_UNKOWN_GLYPH,      L"Warning Unknown Glyph"},
      |     ^~~~~~~~~~~~~~~~~~~~~
      |     EFI_WARN_UNKNOWN_GLYPH
make[2]: *** [<builtin>: console.o] Error 1
make[2]: *** Waiting for unfinished jobs....

Backport upstream commit d230d02f990f02293736dca78b108f86c86d1bd0 to
resolve this issue.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>