pnp: isapnp: Export isapnp_read_byte again

The build of drivers/staging/gpib/hp_82341 driver was failing
with:

ERROR: modpost: "isapnp_read_byte"
[drivers/staging/gpib/hp_82341/hp_82341.ko] undefined!

because the symbol was not exported for modules.

There were no errors building with allyesconfig

The symbol was removed by
Link: https://lore.kernel.org/all/[e-mail]/
because it was no longer used by any mainline modules.

Export the symbol again.

Reported-by: Stephen Rothwell <[e-mail]>
Closes: https://lore.kernel.org/r/[e-mail]
Cc: Jaroslav Kysela <[e-mail]>
Cc: Rafael
Cc: Arnd Bergmann <[e-mail]>
Signed-off-by: Dave Penkler <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/pnp/isapnp/core.c

···
 EXPORT_SYMBOL(isapnp_present);
 EXPORT_SYMBOL(isapnp_cfg_begin);
 EXPORT_SYMBOL(isapnp_cfg_end);
+EXPORT_SYMBOL(isapnp_read_byte);
 EXPORT_SYMBOL(isapnp_write_byte);
 
 static int isapnp_get_resources(struct pnp_dev *dev)