board: dhelectronics: Use isascii() before isprint() in dh_read_eeprom_id_page()

board: dhelectronics: Use isascii() before isprint() in dh_read_eeprom_id_page()

The isprint() checks printability across all 256 characters, some of the
upper 128 characters are printable and produce artifacts on UART. Call
isascii() first to only consider the bottom 7bit ASCII characters as
printable, and then check their printability using isprint(). This fixes
a rare misprint in case the ID page content is uninitialized or corrupted.

Signed-off-by: Marek Vasut <marek.vasut@mailbox.org>
Reviewed-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>