Fixes the following warning:
```
/home/daniel/kimageformats/src/imageformats/dds.cpp: In function ‘qfloat16 readFloat16(QDataStream&)’:
/home/daniel/kimageformats/src/imageformats/dds.cpp:1037:11: warning: ‘void* memcpy(void*, const void*, size_t)’ copying an object of non-trivial type ‘class qfloat16’ from an array of ‘quint16’ {aka ‘short unsigned int’} [-Wclass-memaccess]
1037 | memcpy(&f16, &rawData, sizeof(rawData));
| ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/qt6/QtCore/qmetatype.h:14,
from /usr/include/qt6/QtCore/qobject.h:18,
from /usr/include/qt6/QtCore/qiodevice.h:10,
from /usr/include/qt6/QtGui/qimageiohandler.h:9,
from /usr/include/qt6/QtGui/QImageIOPlugin:1,
from /home/daniel/kimageformats/src/imageformats/dds_p.h:13,
from /home/daniel/kimageformats/src/imageformats/dds.cpp:12:
/usr/include/qt6/QtCore/qfloat16.h:46:7: note: ‘class qfloat16’ declared here
46 | class qfloat16
| ^~~~~~~~
```
Should also fixes the following failed tests under PowerPC (32-bits):
```
INFO : rgba16dx10.dds: converting rgba16dx10.dds from RGBA16FPx4 to ARGB32
FAIL : rgba16dx10.dds: differs from rgba16dx10.png
expected data written to rgba16dx10.dds-expected.data
actual data written to rgba16dx10.dds-actual.data
```
```
INFO : rgba_f16.dds: converting rgba_f16.dds from RGBA16FPx4 to ARGB32
FAIL : rgba_f16.dds: differs from rgba_f16.png
expected data written to rgba_f16.dds-expected.data
actual data written to rgba_f16.dds-actual.data
```
