linker: kobject-text: align multiline string definition syntax

Align multiline string definition syntax in ASSERT in linker
script. This allows to use linker script with ASSERT provided
by linker (i.e GNU toolchain) or dummy ASSERT defined as
preprocessor macros (ARC MWDT toolchain).

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>